The proposed studies are intended to uncover the importance of the cyclic GMP system in biological regulation and how this cyclic nucleotide and its related metabolic components participate in the process of controlling certain cell functions. The investigations in this proposal deal with the oxidative-reductive mode of modulating guanylate cyclase activity with particular emphasis on substances such as ascorbic acid, dehydroascorbic acid, fatty acid hydroperoxides and prostaglandin endoperoxides as activators of this cyclase by a mechanism(s) involving oxidation. The cellular components generated in response to hormonal and other biological signals that represent the oxidizing equivalents within the cell which promote activation of guanylate cyclase are being identified and the mechanism by which this enzyme is activated through an oxidative mechanism is being investigated.